How it works
A two-part polyurethane is injected as a liquid through probes or ports into the soil behind the wall. Within seconds it reacts and expands, filling voids and cracks and binding loose soil. The cured foam is closed-cell, so it resists water. Installers use two kinds:
- Two-component foam expands more and is stronger once cured. It's used for larger voids.
- Single-component foam reacts faster but is weaker. It suits known, smaller gaps.
What it's good for
- Soil washing out through joints or small cracks, the usual cause of sinkholes behind a wall.
- Voids behind the panels that haven't yet caused the wall to move.
- Stabilizing soil along the wall as part of a wider repair.
What it can't do
- Fix a failing structure. A wall that leans or bows because the tiebacks or anchors have failed needs structural work or replacement.
- Repair broken panels or a crumbling cap. See seawall cap repair.
- Add height. If local rules or flooding mean the wall must be raised, foam doesn't help.
Things that can go wrong
- Over-injection. Without control of pressure and flow, foam can push the wall or lift the slab behind it.
- Blocked weep holes. Drainage paths that relieve water pressure behind the wall can be sealed by mistake, which loads the wall.
- Inexperienced installers. Results depend heavily on the crew.
What to ask a contractor
- What's causing the soil loss, and is the wall itself sound?
- Which foam, how much, and how will you control pressure?
- How will you keep the weep holes and drainage working?
- What's guaranteed, and for how long?
- Does this need a permit here? See Broward, Lee County or Pinellas permits.
Not sure whether your wall is sound? Start with a seawall inspection. For costs, see the cost guide: targeted repairs like injection sit at the low end of the published ranges.
Sources: installer information from HMI, and US patent 5,911,545 on foam stabilization of seawalls.
This page summarizes published rules and prices for general information. It isn't engineering or legal advice, and codes change. Your contractor, engineer and building department have the final word for your property.
Common questions
Does foam injection fix a leaning seawall?
Not on its own. Foam fills voids and stabilizes soil behind the wall. A wall that's leaning because its tiebacks or anchors have failed needs structural repair, such as new tiebacks, or replacement.
How long does seawall foam last?
Manufacturers and installers claim long lives, and one patent for the method describes a minimum life of ten years. We haven't found independent long-term studies, so treat lifespan claims with care and ask what the contractor guarantees.